If rust-analyzer receives a malformed LSP request, the IO thread
terminates with a meaningful error, but then closes the channel.
Once the channel has closed, the main_loop also terminates, but it
only has RecvError and can't show a meaningful error. As a result,
rust-analyzer would incorrectly claim that the client forgot to
shutdown.
```
$ buggy_lsp_client | rust-analyzer
Error: client exited without proper shutdown sequence
```
Instead, include both error messages when the server shuts down.
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